Chain drive systems are used to operate ancillary components associated with automotive engines. For example, chain drive systems are used to drive complex valve trains, balance shafts, oil pumps, high pressure fuel injection pumps and water pumps.
Known chain drive systems include a chain and a chain drive tensioner system that is operable to create an initial required tension on the chain. However, over time, as the chain of the chain drive system wears, slack is generated in the chain drive system. As the chain wears, it is the chain drive tensioner system that is operable to remove the slack from the system.
Known chain drive tensioner systems generally include a tensioner body and a tensioner piston attached to a shoe. Oil pressure generated within the tensioner body, exerts pressure against the tensioner piston and shoe assembly, which engages the chain to create the required tension. As the chain wears, the tensioner piston extends to remove the slack from the system. However, as the tensioner piston extends, the leverage the chain has on the chain tensioner system increases effectively reducing the chain tensioner system's ability to control the chain drive.
In one known chain drive tensioner system, the tensioner body includes an orifice of a fixed size, which allows for a fixed leakdown of oil pressure within the chain drive tensioner system to control the reaction stiffness of the chain drive tensioner as the chain wears. However, because the leakdown of this system is fixed, the stiffness of the chain tensioner system remains constant throughout the extension range of the tensioner piston while the leverage the chain has on the chain tensioner system increases.